The technical field generally relates to high pressure fuel injectors. High pressure fuel injectors exhibit delay periods after the command of opening and closing of the injector, and additionally can experience variations in the injector response during fuel injection. These variations affect the actual amount of fuel injected versus the commanded amount of fuel, and can additionally affect the emissions performance and torque generation of the engine that utilizes the fuel injector. Direct feedback measurement of the injector opening and closing events and of the fuel injection characteristics is difficult to obtain with commercially reasonable hardware on a production engine. Therefore, further technological developments are desirable in this area.